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United States Patent |
6,039,904
|
Nitta
,   et al.
|
March 21, 2000
|
Method of adjusting a heat-displacing T-die
Abstract
A novel method of adjusting a heat-displacing T-die is provided wherein a
T-die slit gap is adjusted by thermal expansion and contraction of die
bolts individually provided with heaters so that a sheet or film material
has a target profile in thickness, characterized in that a thickness feed
back control loop and a virtual temperature control loop are provided, and
in the thickness feed back control loop, data of thickness of products are
subjected to a profile treatment to correct a target profile for
temperature setting and changing of die bolts so as to define an
appropriate slit gap, and in the virtual temperature control loop, an
appropriate die bolt temperature is predicted from a control output value
of the heater and a radiation temperature to the circumference so as to
calculate a corresponding power to be supplied to the heater.
Inventors:
|
Nitta; Satoru (Shizuoka, JP);
Mizunuma; Koji (Shizuoka, JP)
|
Assignee:
|
Toshiba Machine Co., Ltd. (Tokyo, JP)
|
Appl. No.:
|
025444 |
Filed:
|
February 17, 1998 |
Foreign Application Priority Data
Current U.S. Class: |
264/40.5; 425/141 |
Intern'l Class: |
B29C 047/00 |
Field of Search: |
264/40.5,40.1,177.16
425/141,466
364/475.01
|
References Cited
U.S. Patent Documents
3940221 | Feb., 1976 | Nissel | 425/141.
|
4454084 | Jun., 1984 | Smith et al. | 264/40.
|
4592710 | Jun., 1986 | Reifenhauser et al. | 425/141.
|
4594063 | Jun., 1986 | Reifenhauser et al. | 425/141.
|
4931982 | Jun., 1990 | Hayashida et al. | 364/473.
|
4978289 | Dec., 1990 | Maejima | 425/141.
|
4994976 | Feb., 1991 | Akasaka | 364/473.
|
5622730 | Apr., 1997 | Nitta et al. | 425/141.
|
Primary Examiner: Silbaugh; Jan H.
Assistant Examiner: Eashoo; Mark
Attorney, Agent or Firm: Whitham, Curtis & Whitham
Claims
What is claimed is:
1. A method of adjusting a heat-displacing T-die, wherein a T-die slit gap
is adjusted by thermal expansion and contraction of die bolts individually
provided with heaters so that a sheet or film material has a target
profile in thickness, the method comprising the steps of:
providing a thickness feed back control loop, wherein the thickness feed
back control loop calculates a target profile adjustment for the die bolts
so as to define a spacing of the T-die slit gap based on a deviation
between the target profile in thickness and a measured thickness profile
of the sheet or film material;
providing a virtual temperature control loop, wherein the virtual
temperature control loop predicts a temperature of the die bolts based on
a control output value of the heaters and a radiation temperature to the
circumference of the die bolts so as to calculate a power to be supplied
to the heaters; and
controlling the die bolt temperature by supplying the power to the heaters
thereby adjusting the T-die slit gap based on the steps of calculating a
target profile adjustment and predicting the die bolt temperature.
2. The method of claim 1, wherein providing the thickness feed back control
loop further comprises:
setting the target profile in thickness prior to forming the product;
processing the thickness profile of the product after the setting the
target profile; and
providing the thickness profile to an input of the thickness feed back
control loop in the step of providing the thickness feed back control
loop.
3. The method of claim 1, wherein the target profile adjustment for the die
bolts is calculated from the deviation between the target profile and the
thickness profile inputted by a feed back to the thickness feed back
control loop.
4. The method of claim 1, further comprising calculating a renewal
temperature from a calculated amount of the target profile adjustment for
the die bolts so that an insurrection signal is outputted for change in a
setting temperature of a die bolt heater temperature control unit.
5. The method of claim 1, wherein providing the virtual temperature control
loop includes:
receiving a setting temperature for the die bolts;
controlling the temperature of the die bolts based on the setting
temperature, the temperature being controlled by adjusting the power of
the heaters; and
predicting and calculating a predicted temperature of the die bolts based
on the temperature output from the controlling step, and wherein the
temperature is calculated from a difference between the predicted
temperature and the setting temperature.
6. The method of claim 5, wherein providing the virtual temperature control
loop further includes periodically repeating the steps of claim 5.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method of adjusting a heat-displacing
T-die for sheet formation and film formation, and more particularly to a
method of adjusting a heat-displacing T-die to permit convenient and
proper profile control of sheets and films by cascade control to a lip
adjusting amount of the T-die in a virtual temperature adjusting loop for
estimation and operation on the basis of control output data of a
heat-displacing actuator and a thickness feed back control loop calculated
from data of thickness of formed products.
In general, a heat-displacing T-die having a structure as shown in FIG. 1
is used for sheet formation and film formation. The heat-displacing T-die
has a body 10. A T-die lip 14 is formed as a part of the body 10 of the
heat-displacing T-die. The T-die lip 14 has a slit gap 12 for extrusion
molding of a molten resin into the shape of a sheet. A large number of die
bolts 16 are further provided which extend in a direction along which the
slit gap 12 is formed, so that the die bolts 16 are made into contact with
the T-die lip 14. Each of the die bolts 16 is provided with a
temperature-adjustable heater 18 which is electrically connected to a
cable 20 for supplying a controlled current to the heater 18. Another
heater 22 is provided on a top surface of the body 10 of the
heat-displacing T-die for temperature control of the body 10. Inside of
the T-die lip 14, a flexible necked down portion 14a is formed in the body
10.
The slit gap 12 of the T-die lip 14 is adjusted by thermal expansion of the
die bolts 16 having received a heat from the heater 18.
There are known in the art a heat direct-acting type and a heat
reverse-acting type.
As illustrated in FIG. 2, the heat-displacing T-die of the heat
direct-acting type has the following structure. A heater holder 18 is
provided for holding the die bolt 16. The heater holder 18 holes a first
end portion 16a of the die bolt 16 near the T-die lip 14, so that a
temperature rising of the heater 18 causes an expansion of the die bolt 16
toward the T-die lip 14 whereby the first end portion 16a of the die bolt
16 presses down the T-die lip 14. As a result, the slit gap 12 of the
T-die lip 14 is narrowed.
As illustrated in FIG. 3, the heat-displacing T-die of the heat
reverse-acting type has the following structure. A heater holder 18 is
provided for holding the die bolt 16. The heater holder 18 holds a second
end portion 16b of the die bolt 16 opposite to the first end portion 16a
near the T-die lip 14, so that a temperature rising of the heater 18
causes an expansion of the die bolt 16 in a direction opposite to the
direction toward the T-die lip 14 whereby the second end portion 16b of
the die bolt 16 is withdrawn from the T-die lip 14. As a result, the slit
gap 12 of the T-die lip 14 is widened.
In the prior art, as the method of adjusting the heat-displacing T-die, a
feed back system of FIG. 4 and a cascade system of FIG. 5 have been known.
In accordance with the feed back system of FIG. 4, a target profile is
transmitted through a profile control unit 30, a die bolt heater control
unit 32, and a die bolt-lip system 34 to a forming processor 36 for
profile control of a sheet. The result of the profile control is then
processed in a profile processor 38 so as to be fed-back to the profile
control unit 30. Those feed back control and operations are carried out at
a constant period. A power to be supplied to the heater of the die bolt is
renewed step-like. As a result, a thickness of the sheet at a
correspondence position is exponentially increased and then reaches an
equilibrium state, during which it takes a time of a few times as long as
a time constant of the heater. The above variation can be detected after
an unnecessary time L has been passed. For this reason, a vibration in the
shape of a saw-tooth is likely to appear in the profile due to overshoot.
Since the influence by external disturbance can be detected only by a
thickness gauge, a correct operation to the externally disturbed D1 to D4
is late thereby making it difficult to improve the accuracy of the
adjustment.
FIG. 5 is illustrative of the cascade system wherein the target profile is
transmitted through a profile control section 40, a temperature control
section 41, a die bolt heater control unit 42 and a die bolt-lip system 44
to a forming processor 46 for profile control of the sheet. In this case,
the temperature of the heater is detected, so that the detected
temperature value is then fed back to the temperature control unit 41. The
result of the profile control made by the forming process is then
processed by a profile processing unit 48 for feeding the same back to the
profile control unit 40 for performing a cascade control so that the
temperature to be set for each die bolt is renewed by step like and a
power to be supplied to the heater is adjusted.
It is, for example, disclosed in the Japanese Patent Publication No.
1-22140 that processing is made for the mutual thermal interference
between adjacent die bolts to calculate the temperature having been newly
set for each die bolt so that an initial die bolt temperature having
previously been set, which provides no temperature influence to the
material, is compared to an average of all of the newly set die bolt
temperature calculated so that the average is adjusted to correspond to
the initial die bolt temperature whereby a heat-displacing T-die slit gap
is adjusted in the vicinity of an optimum temperature for forming the
material.
In the cascade control system, a slave loop for the die bolt temperature is
provided in a master loop for the profile as illustrated in FIG. 5, for
which reason the die bolt temperature having been set is renewed step like
by an instruction of the master loop whereby PID operation is effected for
quick correction. D1 and D2 in the external disturbances are almost
completely processed in the slave loop, resulting in remarkable
improvements in responsibility and stability.
In the above conventional feed back system, the temperature of the heater
of the heat-displacing T-die is not detected and a control to the heater
is decided directly from the thickness deviation, for which reason the
following advantages and disadvantages are caused.
It is advantageous that since no temperature sensor is provided, the heater
has a simple structure and the control unit with one loop is also simple.
It is, however, disadvantageous that it takes a long time for movement to
the thickness gauge of the sheet extruded from the heat-displacing T-die.
The displacement of the T-die lip is caused by thermal expansion of
contraction of the die bolt due to a temperature variation of the heater.
Even if the power to be supplied to the heater is kept constant, then the
temperature is varied.
In the above cascade system, in order to improve the disadvantages of the
feed back system, a temperature sensor is provided for the die bolt
provided with the heater for temperature control of individual die bolt.
This cascade system has the following advantages and disadvantages.
It is advantageous that since in order to detect and manage the temperature
of the heater, variation of the heat-displacing T-die slit is predictable
directly from the detected value of the die bolt temperature, a
temperature control loop can be set in a constant time regardless of an
unnecessary time from the heat-displacing T-die from the thickness gauge.
It is, however, disadvantageous that a temperature sensor is provided for
each die bolt whereby the structure is complicated and the wiring of leads
between to the heater and the sensor is also complicated. As a result, the
manufacturing cost thereof is increased.
In the above circumstances, it had been required to develop a novel method
of adjusting a heat-displacing T-die in a cascade system of a temperature
control loop and a thickness feed back control loop free from the above
disadvantages.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a novel
method of adjusting a heat-displacing T-die in a cascade system of a
temperature control loop and a thickness feed back control loop, free from
the above disadvantages.
It is a further object of the present invention to provide a novel method
of adjusting a heat-displacing T-die in a cascade system of a temperature
control loop and a thickness feed back control loop, wherein a temperature
of the die bolt is predicted from the past heater control output value and
a radiation temperature to the circumferences of the heater is provided so
that a corresponding heater control output value is calculated in a
virtual temperature control loop whereby a profile control of the sheet is
simply and properly carried out without use of a temperature sensor.
The above and other objects, features and advantages of the present
invention will be apparent from the following descriptions.
In accordance with the present invention, a novel method of adjusting a
heat-displacing T-die wherein a T-die slit gap is adjusted by thermal
expansion and contraction of die bolts individually provided with heaters
so that a sheet or film material has a target profile in thickness,
characterized in that a thickness feed back control loop and a virtual
temperature control loop are provided, and in the thickness feed back
control loop, data of thickness of products are subjected to a profile
treatment to correct a target profile for temperature setting and changing
of die bolts so as to define an appropriate slit gap, and in the virtual
temperature control loop, an appropriate die bolt temperature is predicted
from a control output value of the heater and a radiation temperature to
the circumference so as to calculate a corresponding power to be supplied
to the heater.
BRIEF DESCRIPTION OF THE DRAWINGS
Preferred embodiments according to the present invention will be described
in detail with reference to the accompanying drawings.
FIG. 1 is fragmentary cross sectional elevation view illustrative of the
heat-displacing T-die to be used for sheet formation and film formation.
FIG. 2 is fragmentary cross sectional elevation view illustrative of the
heat-displacing T-die of the heat direct-acting type.
FIG. 3 is fragmentary cross sectional elevation view illustrative of the
heat-displacing T-die of the heat reverse-acting type.
FIG. 4 is a block diagram illustrative of a feed back system for adjusting
the heat-displacing T-die.
FIG. 5 is a block diagram illustrative of a cascade system for adjusting
the heat-displacing T-die.
FIG. 6 is a block diagram illustrative of a system for adjusting a
heat-displacing T-die.
FIG. 7A is a flow chart illustrative of operations of the thickness feed
back control in the profile control unit and the thickness profile
processing unit.
FIG. 7B is a flow chart illustrative of operations of the in the virtual
temperature control loop by the die bolt heater control unit, the heater
control output device and the die bolt heater temperature prediction and
calculation unit.
FIG. 8A is a graph illustrative of a variation in thickness of the sheet.
FIG. 8B is also a graph illustrative of deviation of the thickness of the
sheet over individual die bolts.
FIG. 8C is a graph illustrative of variations in die bolt heater
temperature of individual die bolts, wherein white bars represent the
setting temperatures and black bars represent the predicted temperatures.
PREFERRED EMBODIMENTS
FIRST EMBODIMENT
A first embodiment according to the present invention will be described in
detail with reference to the drawings. A method of adjusting a
heat-displacing T-die is provided. FIG. 6 is a block diagram illustrative
of a system for adjusting a heat-displacing T-die.
A target profile is transmitted through a profile control unit 50, a die
bolt heater temperature control unit 52, a heater control output unit 53
using, for example, a solid state relay and a die bolt-lip system 54 to a
forming process 56 for sheet profile control or adjustment. The
heat-displacing T-die as illustrated in FIGS. 1 and 3 is also available in
the present invention.
The virtual temperature control loop is provided wherein the temperature of
the die bolt is predicted by the die bolt heater temperature control unit
52 from the heater control output value outputted from the heater control
output unit 53 and the radiation temperature to the circumference for
feeding the same back to the die bolt heater temperature control unit 52.
Similarly to the conventional cascade control, the thickness feed back
control loop is provided, wherein the result of the profile control from
the forming process 56 is then processed in the thickness profile
processor 58 for feeding the same back to the profile control unit 50.
Operations of the thickness feed back control in the profile control unit
50 and the thickness profile processing unit 58 will be described with
reference to FIG. 7A.
In the step 1, a target profile is set for the profile control unit 50. In
the step 2, a thickness profile processed in the thickness profile
processing unit 58 is fed back for input. In the step 3, the control
timing is verified. In the step 4, an amount of the adjustment of the die
bolt is calculated from the deviation of the target profile and the
thickness profile inputted by the feed back. In the step 5, a renewal
temperature is calculated from the calculated amount of the adjustment of
the die bolt so that an insurrection signal is outputted for change in
setting temperature of the die bolt heater temperature control unit 52.
Thereafter the profile control unit 50 waits for control operation until
the next control timing comes before the above operations will repeat.
Subsequently, operations of the in the virtual temperature control loop by
the die bolt heater control unit 52, the heater control output device 53
and the die bolt heater temperature prediction and calculation unit 55
will be described with reference to FIG. 7B.
In the step 6, the initial setting temperature of the die bolt is inputted
to the die bolt heater temperature control unit 52. In the step 7, an
instruction is made by the profile control unit 50 to change the setting
temperature at a predetermined timing. In the step 8, the setting
temperature is changed whereby the heater control output unit 53 controls
the heater for temperature control of the individual die bolts.
If the setting temperature has been changed or no change to the setting
temperature has been made, a prediction and calculation of the die bolt
temperature is executed in the die bolt heater temperature prediction and
calculation unit 55 on the basis of the heater control output value from
the heater control output unit 53 in the step 9. A PID operation is made
to calculate the heater controlling output value from a difference between
the predicted temperature and the setting temperature in the step 10.
The heater control output value calculated thereby is then sent through the
die bolt heater temperature control unit 52 and outputted from the heater
control output unit 53 for control the temperature of the heater to
control the temperature of the individual die bolt in the step 11.
In the step 2, the temperature control timing for operation of the heater
control output value is appropriately set for the repeat of the above
sequential control operations.
The above prediction and operation of the heater control output value in
the die bolt heater temperature prediction and calculation unit 55 will be
described in more detail.
The temperature of the die bolt is decided on the basis of a quantity Q0 of
a radiation heat to the circumference and a quantity Q1 of the heat
generation as the past heater control output value. In this case, since
many die bolts are arranged in parallel to each other, then a quantity QB
of the heat is also transmitted from the adjacent die bolt.
The quantity Qi of the heat generation of the heater is given by the
following equation.
Qi=C1.times.(.theta.h-.theta.i) (1)
where C1 is the conductance of the heat, .theta.h is the temperature of the
heater and .theta.i is the temperature of the die bolt.
On the other hand, the quantity QB of the heat from the adjacent die bolt
is given by the following equation.
QB=C2i.times.(.theta.(i-1)-.theta.i)+C2i.times.(.theta.(i+1)-.theta.i)(2)
where C2 is the conductance of the heat, .theta.i is the temperature of the
die bolt, and .theta.(i-1), .theta.e (i+1) are the temperatures of the
adjacent die bolts.
The quantity Q0 of the heat radiation from the heater to the circumference
is given by the following equation.
Q0=C3.times.(.theta.i-.theta.a) (3)
where C3 is the conductance of the heat, .theta.a is the ambient
temperature around the die bolt heated by the heater, provided .theta.a is
approximated to be 0 for facilitation of the analysis.
In the light of the steady heat conduction, the quantity Q0 of the heat
radiation is given by the following equation.
Q0=Qi+QB (4)
The above equations (1), (2), and (3) are substituted for the above
equation (4) and the following equation is given.
.theta.i=C1/(C1+C3+2C2).times..theta.h+C2/(C1+C3+2C2).times.[.theta.(i+1)+.
theta.(i-1)] (5)
The equation (5) is estimated to be as follows.
.theta.i=G1.times..theta.h+G2.times.[.theta.(i+1)+.theta.(i-1)](6)
where G1 and G2 may be experimentally determined to be numerical.
In the manner as described above, the prediction of the temperature of the
die bolt is made so that a new control output value to the heater is
calculated under the PID control from the deviation of the setting
temperature for sending the same to the heater control output unit 53 for
proper temperature control of the die bolt.
The virtual temperature control loop conducts a prediction and calculation
on the basis of the control output data of the heat-displacing actuator in
a constant period of, for example, 10-30 seconds. The temperature of the
individual die bolt can be set and changed by the thickness feed back
control loop based upon the signals from the thickness gauge at a control
timing of, for example, 2-5 minutes.
FIG. 8A is a graph illustrative of a variation in thickness of the sheet.
FIG. 8B is also a graph illustrative of deviation of the thickness of the
sheet over individual die bolts. FIG. 8C is a graph illustrative of
variations in die bolt heater temperature of individual die bolts, wherein
white bars represent the setting temperatures and black bars represent the
predicted temperatures. The correspondence between the white and black
bars means an ideal state free of any external disturbance.
Whereas modifications of the present invention will be apparent to a person
having ordinary skill in the art, to which the invention pertains, it is
to be understood that embodiments as shown and described by way of
illustrations are by no means intended to be considered in a limiting
sense. Accordingly, it is to be intended to cover by claims all
modifications which fall within the spirit and scope of the present
invention.
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